Janet : Some old lenses were doped with radioactive elements to modify their refractive properties, so that the lenses themselves became radioactive. Over time the radioactive elements decayed and the lenses became yellow as a result of radiation dmage (I think; I'm not sure of the EXACT mechanism of the yellowing). For example, a lot of the Olympus 55mm f/1.2 lenses have this. i don't own one but I own its successor, the 50mm f/1.2.The 55mm f/1.2 comes up on eBay occasionally, around £250 in good condition. So it is very possible that Mocha's disapproval had caused some discolouration of the face that emits it!